Heating, ventilating and air conditioning (HVAC) systems can be used to regulate the environment within an enclosed space. Typically, an air blower is used to pull air from the enclosed space into the HVAC system through ducts and push the air back into the enclosed space through additional ducts after conditioning the air (e.g., heating, cooling or dehumidifying the air). Various types of HVAC systems may be used to provide conditioned air for enclosed spaces. For example, some HVAC units are located on the rooftop of a commercial building. These so-called rooftop units, or RTUs, typically include one or more blowers and heat exchangers to heat and/or cool the building, and baffles to control the flow of air within the RTU. Some RTUs also include an air-side economizer that allows to selectively provide fresh outside air to the RTU or to recirculate exhaust air from the building back through the RTU to be cooled or heated again.
When the enthalpy of the fresh air is less than the enthalpy of the recirculated air, conditioning the fresh air may be more energy-efficient than conditioning the recirculated air. In this case the economizer may exhaust a portion of the stale air and replace the vented air with outside air. When the outside air is both sufficiently cool and sufficiently dry it may be possible that no additional conditioning of the outside air is needed. In this case the economizer may draw a sufficient quantity of outside air into the building to provide all the needed cooling. In some installations an energy recovery ventilator (ERV) may be used to pre-condition the fresh air demanded by the RTU. The ERV may include, e.g., an enthalpy exchange zone to transfer heat and/or humidity between an incoming fresh air stream and an outgoing exhaust air stream. The enthalpy exchange zone can include one or multiple enthalpy wheels. ERVs are typically equipped with fresh-air and return air filters that allow energy recovery from areas, such as kitchens and smoking area, that have a high level of contaminants but can still benefit from fresh-air. As such, using filters, even in areas with low contaminant levels, reduces the need for cleaning an enthalpy wheel according to a typical maintenance/service plan.
Thus, RTUs and HVAC systems in general have been improved with various options, such as an ERV, to provide higher efficiency and better comfort. Accordingly, HVAC systems have typically become more complex resulting in a cost increase for installation and service.